Several constructions of such loppers are known, and many constructions commonly having a construction comprising an elongated pole having an upper end to which a lopping assembly is mounted, comprising a movable knife and a counter knife which possibly is also movable, and which are movable in a direction towards one another, the movable knife and the counter knife being held in the open position by resilient means and are movable in a direction towards one another in a cutting direction by a force exerted thereon by actuating means disposed in the region of the lower end of the rod via a transmission and connection means.
The transmission and connection means may be formed by pull cables, gears and/or chain gear arrangements.
It is known that on cutting of wood, depending on the geometry of the cutting edge of the knife, mostly in the middle region or near the end of the cutting process, an increase of the cutting forces occurs, which are compensated by these means, thereby are adapted to the strength of the user.
On this reason, shears for cutting of branches or of underwood are known which do not operate in the course of the cutting action with a constant transmission ratio between the movement of the cutting edge of the knife and the actuation force.
From the DE 816616, an example of a lopper is known wherein transmission and connection means are formed by a pull cable drive having a first end attached to a crank lever connected to the movable knife, wherein the pull cable attached the crank lever approaches a substantially perpendicular position relative to the longitudinal axis of the crank lever or lever arm on approaching closed position of the knifes. In this manner, the shearing force increases continuously on progressively approaching the closed position of the knifes, such that the cutting of even thicker branches is facilitated. The actuating means disposed at the lower end of the pole is formed by a lever transmission having a load arm connected to the knifes via pull cable hoist of the type of a block and tackle system and having a force arm formed by a pivotable lever.
Further, loppers or pruning shears are known which use for instance a change of a handle length or a change of the coupling position of linkages for obtaining adjustable transmission ratios.
DE 101 30 452 A1 discloses a lopper comprising a gear box switchable between at least two gear shift positions within the force transmission path from the lopping assembly to the actuating means. The switching between the gear box transmission ratios is performed by means of control elements within the region of the lopping assembly.
U.S. Pat. No. 4,760,645 discloses a lopping assembly of lopper wherein the variation between two or more transmission ratios of a transmission and connection means between the movable knifes and a pull rope is obtained by an adjustable variation of the length of a lever arm forming part the movable knife. Also in this case, the switchover between the gear box positions is performed via elements disposed in the region of the lopping assembly so that the lopper first has to be removed from the tree.
The DE 561668 discloses a lopper wherein a movable knife of the lopping assembly is connected to via toothed wheels to a lever arm having a free end which is connected via a pull cable to an actuating means, both the toothed wheels as well as the pull rope provide a transmission resulting in reduction of the force exerted on the actuating means relative to the force acting on the lopping assembly.
Further, U.S. Pat. No. 2,744,322 discloses lopper or pruning shears wherein the free end of a connection rod is connected to the lever arm of a movable knife. The actuation means is formed by a sliding sleeve surrounding the lower end of the rod and connected by a pull cable drive of the type of a sheave or block and tackle system to the lower end of the connection rod.
Both the pull cable drive as well as the actuation rods may be disposed within a hollow tube forming the pole and extend through this hollow rod, or they may be disposed closely adjacent to the pole on the outer side thereof. The pole itself may be a telescopic pole to allow an adaption to the height position of the branch or the like to be cut.